The present invention relates to a combined lean burn and stoichiometric fuel control for an automotive internal combustion engine.
Engine air-fuel ratio control typically uses an exhaust gas oxygen sensor for feedback control. One system shows a xe2x80x9clinearxe2x80x9d exhaust gas sensor upstream of catalyst and a xe2x80x9cswitchingxe2x80x9d exhaust gas sensor downstream of the catalyst. In this system, the xe2x80x9cswitchingxe2x80x9d sensor is used to monitor the catalyst and the xe2x80x9clinearxe2x80x9d sensor. Further, the xe2x80x9cswitchingxe2x80x9d sensor is used for air-fuel control during engine start until the xe2x80x9clinearxe2x80x9d sensor reaches its operating temperature. However, whenever the xe2x80x9clinearxe2x80x9d sensor attains the activation temperature, it is utilized to control engine air-fuel ratio. Such a method is described U.S. Pat. No. 5,832,724.
The inventors herein have recognized a disadvantage of the above approach. In particular, the xe2x80x9clinearxe2x80x9d sensor has less accuracy in determining the point of stoichiometry than the xe2x80x9cswitchingxe2x80x9d sensor. This is generally because the xe2x80x9clinearxe2x80x9d sensor is designed to provide a signal indicative of actual air-fuel ratio over a wide air-fuel ratio range, whereas the xe2x80x9cswitchingxe2x80x9d sensor is designed to produce a very large change (xe2x80x9cswitchxe2x80x9d) at the point of stoichiometry. Thus, when operating near stoichiometry, such a system provides degraded performance.
Disadvantages of prior approaches are overcome by a system for controlling engine air-fuel ratio entering an emission control device comprising: a switching exhaust gas sensor located downstream of the emission control device; a linear exhaust gas sensor located upstream of the emission control device; and a controller adjusting a fuel injection amount into the engine based on both said switching exhaust gas sensor and said linear exhaust gas sensor when operating near stoichiometry; and adjusting said fuel injection amount into the engine based on said linear exhaust gas sensor and independent of said switching exhaust gas sensor when operating away from stoichiometry.
By utilizing both the switching sensor and linear sensor when operating near stoichiometry, it is possible to improve the accuracy of the air-fuel ratio control system. Further, with the same system, it is possible to retain a linear sensor to provide accurate air-fuel ratio control away from stoichiometry.
An advantage of the above aspect of the present invention is improved emissions and improved fuel economy.